The present invention relates to microdevices and, in particular, to a microdevice using a high molecular weight polymer to deflect a membrane.
In the past decade many low voltage electromechanical microactuators based on electrostatic, magnetic, bimorph, thermopneumatic, and shape-memory forces have been developed. A parameter that characterizes the ability of an electromechanical actuator to exert work on a load is its actuation energy. Actuation energy is defined as the product of actuator force times minimum displacement. Preferably, actuators can be scaled and operate under various conditions. A more suitable parameter, energy density Pa, is the actuation energy divided by the total actuator volume, when the actuator is operated under low voltages.
The table below shows Pa values for several different low voltage microactuators. The majority of these devices can provide either a large deflection without a large force or vice-versa. From Table 1 below, it is clear that electrostatic actuators have the lowest energy density and thermal actuators have the highest energy density. Among these, thermopneumatic microactuators and shape memory alloy (SMA) microactuators develop the largest energy density, Pa. These latter two microactuators convert electrical to mechanical work through a high density working substance.
SMAs provide very large forces, but their linear deformation strain is limited to about 8%. Therefore, SMAs often use mechanical advantage schemes to increase displacement. Thermopneumatic actuators provide both large displacements and forces, but their fabrication and integration into large microsystems is often cumbersome. This is due to the difficulty of encapsulating the working substance, typically a liquid, into a sealed cavity.
The working substance in a microactuator, however, can be a solid. A desired general property of a solid working substance is a large thermal expansion range at the solid-liquid phase transition. Typically, this property is found in long chained polymers. Paraffins are long chained polymers which have this large thermal expansion characteristic plus a low transition temperature which is also a desired property. Thus, long chained polymers including paraffins, have the ability to generate very large energy density Pa actuators. Such polymers are hereinafter defined as xe2x80x9chigh actuating power polymersxe2x80x9d or HAPP. Macroscopic paraffin actuators have been developed for many applications including automotive thermostats and more recently in satellite antenna positioning systems and medical devices. As with conventional thermopneumatic actuators, once the polymer melts it transmits pressure, a useful hydraulic property for force and deflection multiplication. These two properties make HAPP actuators particularly attractive for the fabrication of microactuators or simple integrated miniature valves in microfluidic systems.
Over the past decade, elaborate microfluidic valves have also been constructed based on electrostatic, magnetic, piezoelectric, bimorph and thermopneumatic actuation methods. Because of their complexity, the majority of these devices are made by bonding many thick glass or silicon substrates together, some even requiring external cavity fills for the working fluid. This complexity makes for a bulky device and makes these valves large and difficult to integrate with other components in microfluidic systems.
Applications requiring many active microfluidic devices such as valves and actuators on a single die are rapidly emerging. Integrated microgas chromatography and mass spectrometry systems are being developed which require effective microdevices. In addition, microfluidic systems, such as DNA analysis systems, require microvalves in order to control the transport of samples and reagents throughout different parts of the system. Typically these systems require many, independently operating microvalves and microactuators in order to perform complex or parallel functions.
Therefore, what is needed is a microfluidic device that uses a high actuating power polymer and which overcomes the above disadvantages. Specifically, a microdevice is needed that uses simple micromachining fabrication techniques to incorporate a high actuating power polymer that can be patterned using micromachining techniques without requiring any working fluid filling or post-processing sealing operations. Additionally, a microdevice that produces a large deflection and a large force that is easily integrated into microsystems and which can be easily integrated with other fluidic components and that will provide a microdevice which operates independently of other devices, is also desired. It is therefore an object of the present invention to provide a microfluidic device and process for fabricating the device using a high actuating power polymer (HAPP) with these features.
In accordance with the teachings of the present invention, a high actuating power polymer (HAPP) for use in a microfluidic device and its method of fabrication are disclosed. The HAPP, when melted, undergoes a volumetric expansion and/or a phase change in a constrained volume to produce a large deflection and force which is used to move or control an object.
In one preferred embodiment, a microfluidic device is adapted for use with a power source. The device includes a substrate with a heater member. The substrate and heater member form a first portion. A second portion is adjacent to the first portion. The second portion includes a HAPP portion, at least one resin layer and a shield member. The second portion is selectively shaped to form a thermal expansion portion. A diaphragm member encapsulates the thermal expansion portion so that when power is applied to the heater portion, the HAPP portion expands against the diaphragm member and deflects.
In another preferred embodiment, a process for forming a microfluidic device on a substrate is disclosed. The microfluidic device is adapted for use with a power source. The process includes forming a heater on the substrate. The heater portion and the substrate form a first portion. Then, a second portion adjacent to the first portion is constructed. The second portion includes a HAPP layer, at least one resin layer on the HAPP layer and a mask on the resin layer. Next, the second portion is shaped to form a thermal expansion portion. The thermal expansion portion is encapsulated with a diaphragm so that when power is applied to the heater portion, the HAPP layer expands against the diaphragm member so that the diaphragm member deflects.
It is an object of the present invention to provide a microfluidic device that uses a long chained polymer which, when melted, undergoes a large volumetric expansion and/or phase change in a constrained volume to produce a deflection to form an actuator member.
It is another object of the present invention to provide a microfluidic device that uses HAPP which, when melted, undergoes a large volumetric expansion and/or phase change in a constrained volume to form a blocking microvalve.
It is still another object of the present invention to provide a microfluidic device that uses HAPP which, when melted, undergoes a volumetric expansion and/or phase change in a constrained volume with support posts to produce a large deflection in a membrane which operatively engages an outlet port in a reservoir.
These and other objects of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.